346 ANATOMY OF THE GYMNOSPERMS 



South Carolina and southward near the coast to the Florida Keys ; westward 

 along the Gulf coast to the Pearl River, Louisiana, not more than 50 or (10 

 miles inland ; also in the West Indies (Sargent) ; Bahamas and Isle of 

 Pines (Shaw). 



B. PITYOXYLON (Pinoxylon) 



Fossil Species Only 



42. P. dacotense, Knowlton 



" Transverse. Annual rings broad and very distinct, even to the naked 

 eye, being 2-4.5 mm. in width. Distinction between the spring and 

 autumn wood very plain, the former appearing as broad, white bands, 

 and the latter as dense black bands of varying width. Under the micro- 

 scope the line of demarcation between fall and spring wood is observed 

 to be very sharp indeed. The fall wood consists of thick-walled cells 

 of an elliptical or oblong outline, rather loosely placed. The succeeding 

 spring wood is composed of very large cells with relatively thin walls. 

 The medullary rays are long and quite thick-walled. There are no resin 

 cells in the wood. The resin passages are present and quite numerous. 

 They do not seem to be confined to any particular portion of the ring, 

 but are scattered, being perhaps most numerous in the fall wood. They 

 are of relatively large size and lined with thin-walled epithelium. 



" Radial. The walls of the spring and summer wood have 2 rather irreg- 

 ular rows of large, bordered pits. In rare cases these pits are in a single 

 row. The average size of the outer circle is .025 mm., that of the inner 

 circle about .015 mm. The cells of the rays are rather long, covering 

 the width usually of some 4 or more cells of the spring wood. They 

 are rather thick-walled, the walls being strongly dentate or somewhat 

 irregularly thickened. The ray cells are provided with a few scattered, 

 bordered pits, usually only i to the width of a spring cell of the wood, 

 although not rarely there are 2 in a similar width. They are always in i 

 row on the ray cell. 



" Tangential. Medullary rays in a single, superimposed series, from i to 

 rarely 30 cells, the average being from 5 to 12 cells high. None of the 

 rays in the sections examined are of the fusiform type or contain resin 

 passages. The wood cells are, as far as can be made out, without pits 

 or markings of any kind" (Knowlton). 



Trunks of medium size ; material silicified. 



Upper (?) Jurassic near Sturgis, South Dakota (Knowlton). 



43. P. Aldersoni, Knowlton 



" Transverse. The annual rings are very distinct, being plainly discernible 

 to the naked eye. Some of the broadest rings are fully 9 mm. wide and 

 none less than 6 mm. The demarcation between fall and spring wood 

 is very pronounced, the cells of the fall wood being small, compressed, 

 and thick-walled, while those of the early spring wood are very large, 

 and, of course, thin-walled. The cells of the spring and summer wood 

 continue for a width of 5 mm., but little, if any, diminished in size. 



